FIG. 7 is a block diagram which shows a conventional power generation control apparatus together with an electric generator ACG.
In FIG. 7, the electric generator ACG is composed of a stator coil 1, a field coil 2 that is driven to rotate by means of an internal combustion engine (not shown), and a three phase full wave rectifier 3.
The three phase full wave rectifier 3 has an output end A connected to a positive terminal of a battery 5, an electric load 7, and a power generation control device 400, and the field coil 2 is connected to the power generation control device 400.
The power generation control device 400 is provided with an output sensing terminal a, a terminal b for starting (hereinafter referred to as a starting terminal), an external sensing terminal c, an external output terminal d, a terminal e for ground, and a terminal f for field current control.
In the power generation control device 400, the output sensing terminal a is connected to the output end A of the electric generator ACG and the positive terminal of the battery 5, and the starting terminal b is connected to the positive terminal of the battery 5 through a key switch 6. The external sensing terminal c is directly connected to the positive terminal of the battery 5. The terminal f is connected to the field coil 2 of the electric generator ACG, and the terminal e is grounded, together with the three phase full wave rectifier 3.
The power generation control device 400 is provided with a series circuit which is composed of a transistor 401 for switching (hereinafter referred to as a switching transistor 401) and a reflux diode 402 which are inserted between the output sensing terminal a and the terminal e so as to conduct and interrupt a field current to the field coil 2.
From the external output terminal d of the power generation control device 400, an electric potential, which is obtained by voltage dividing the electric potential of the terminal f by resistances 403, 404, is outputted as a signal which is in synchronization with a field current control signal from the terminal f.
In addition, the power generation control device 400 is provided with a NOR circuit 405 connected to a gate terminal of the switching transistor 401, comparators 406, 407 connected to an input terminal of the NOR circuit 405, resistances 408, 409 which serve to voltage divide a reference power supply voltage V thereby to generate an inverting input voltage (−) to the comparator 406, resistances 412, 413 which serve to voltage divide the voltage of the external sensing terminal c thereby to generate a noninverting input voltage (+) to the comparator 406, resistances 410, 411 which serve to voltage divide the reference power supply voltage V thereby to generate an inverting input voltage (−) to the comparator 407, resistances 414, 415 which serve to voltage divide the voltage of the output sensing terminal a thereby to generate a noninverting input voltage (+) to the comparator 407, and, a resistance 416 and a Zener diode 417 which generate the reference power supply voltage V from the voltage of the starting terminal b.
Next, reference will be made to the field current control operation of the electric generator ACG by means of the conventional power generation control device 400 shown in FIG. 7.
First, when the key switch 6 is turned on (closed) to make the starting terminal b of the power generation control device 400 and the batteries 5 conductive with each other, an electric current is supplied from the battery 5 to the inside of the power generation control device 400 through the key switch 6 and the starting terminal b.
As a result of this, the electric current is supplied to the Zener diode 417 by way of the resistance 416 inside the power generation control device 400, so that the reference power supply voltage V of a constant or fixed voltage used as a power supply for the entire circuit inside the power generation control device 400 is generated, thus resulting in a state in which an control operation by means of the power generation control device 400 can be made.
When the power generation control device 400 is placed in the state in which the control operation thereof can be made, the comparator 406 makes a comparison between an input voltage (+) which is obtained by voltage dividing the battery voltage inputted from the external sensing terminal c by the resistances 412, 413, and a reference voltage (−) which is obtained by voltage dividing the voltage of the reference power supply voltage V by the resistances 408, 409.
The comparator 406 outputs a Lo (low) electric potential, in cases where the input voltage (+) is lower than the reference voltage (−), whereas it outputs a Hi (high) electric potential, in cases where the input voltage (+) is equal to or higher than the reference voltage (−).
In addition, the power generation control device 400 is provided with the comparator 407 as a backup when abnormality (a break or disconnection, etc.) occurs in the external sensing terminal c, and the comparator 407 makes a comparison between the input voltage (+) which is obtained by voltage dividing the voltage of the output end A inputted from the output sensing terminal a by the resistances 414, 415, and the reference voltage (−) which is obtained by voltage dividing the voltage of the reference power supply voltage V by the resistance 410 and the resistance 411.
The comparator 407 outputs a Lo electric potential in cases where the input voltage (+) is lower than the reference voltage (−), and outputs a Hi electric potential in cases where the input voltage (+) is equal to or higher than the reference voltage (−).
As described above, in the conventional power generation control device 400, the output potential of the comparator 406 with respect to the external sensing terminal c and the output potential of the comparator 407 with respect to the output sensing terminal a are used for the gate terminal of the one switching transistor 401.
At this time, it is constructed such that a target voltage value of the power generation voltage based on the reference voltage (−) of the comparator 407 is set to a value higher than a target voltage value based on the reference voltage (−) of the comparator 406, and that the output potentials of the comparators 406, 407 can be controlled through the NOR circuit 405 in a suitable manner.
In other words, only in cases where the output potentials of both of the comparators 406, 407 are low (Lo electric potential), the NOR circuit 405 outputs a Hi electric potential thereby to turn on the switching transistor 401, so that a field current is supplied to the field coil 2.
On the other hand, when either one of the output potentials of the comparators 406, 407 becomes high (Hi electric potential), the NOR circuit 405 outputs a Lo electric potential thereby to turn off the switching transistor 401, so that the field current to the field coil 2 is interrupted.
However, a target voltage value of the comparator 407 is higher than a target voltage value of the comparator 406, and hence, in cases where there is no abnormality in the external sensing terminal c, the output potential of the comparator 407 always becomes low (Lo electric potential). Accordingly, the control operation to the switching transistor 401 is not affected, and the control operation of the switching transistor 401 becomes an operation which depends on the output of the comparator 406.
In cases where the battery voltage is in a low state immediately after starting of the internal combustion engine, the input voltage (+) of the comparator 406 becomes lower than the reference voltage (−), so that the comparator 406 outputs a Lo electric potential.
When the comparator 406 outputs a Lo electric potential, the output potential of the NOR circuit 405 becomes high (Hi electric potential), so that a voltage is applied to the gate terminal of the switching transistor 401, thereby placing the source and the drain of the switching transistor 401 in a conductive state.
As a result of this, the field current is supplied from the battery 5 to the field coil 2 by the way of the output sensing terminal a, the switching transistor 401, and the terminal f, so that the magneto motive force of the field coil 2 is thereby increased. In addition, at this time, a high (Hi) electric potential is outputted from the external output terminal d.
In this state, as the rotational speed of the electric generator ACG increases in accordance with the starting of the internal combustion engine, the power generation voltage generated in the stator coil 1 also increases.
The alternating current voltage generated in the stator coil 1 is rectified into a direct current voltage by means of the three phase full wave rectifier 3, so that an electric current is supplied to the battery 5 and the electric load 7.
In accordance with the increase in the power generation voltage of the electric generator ACG, the battery voltage also increases, and so, the input voltage (+) of the comparator 406 increases.
After that, when the input voltage (+) of the comparator 406 becomes higher than the reference voltage (−) so that the comparator 406 outputs a high (Hi) electric potential, the output of the NOR circuit 405 becomes a low (Lo) electric potential, so that the voltage is no longer applied to the gate terminal of the switching transistor 401.
According to this, the conduction between the source and the drain of the switching transistor 401 is put in an interrupted or cut off state, so that the supply of the field current to the field coil 2 is interrupted, as a result of which the magnetomotive force of the field coil 2 reduces and the power generation voltage of the electric generator ACG also decreases. In addition, the electric potential of the external output terminal d at this time becomes a low (Lo) electric potential.
In this manner, the power generation control device 400 carries out field current control on the field coil 2, in such a manner that an electrical energization operation and a cutoff operation for the field current is repeated, whereby the power generation voltage of the electric generator ACG is regulated to the target voltage value, and at the same time, a signal synchronized with the field current control signal from the external output terminal d is outputted to the outside.
In cases where an abnormality such as a break or disconnection of the external sensing terminal c, etc., has occurred in the power generation control device 400 and the field current control by the comparator 406 becomes impossible, the comparator 407 carries out field current control on the output voltage of the electric generator ACG inputted from the output sensing terminal a, similarly to the above-mentioned operation of the comparator 406, thus regulating the power generation voltage of the electric generator ACG to the target voltage value.
Next, reference will be made to a case in which two electric generators each having the power generation control device 400 in FIG. 7 installed thereon are used and operated in parallel to each other at the same time.
FIG. 8 is a block construction view diagrammatically showing a connection state of the conventional electric generators (including the power generation control devices), wherein the connection relation in the case of carrying out the parallel operation of the two electric generators (a main electric generator ACG1 and a subordinate electric generator ACG2) at the same time is shown by only individual terminals.
In FIG. 8, there are shown, in a simplified manner, individual output ends A1, A2 of the main electric generator ACG1 and the subordinate electric generator ACG2, the starting terminal b1, b2, the external sensing terminal c1, c2 and the external output terminal d1, d2 of the individual power generation control devices 400 (refer to FIG. 7) for the main electric generator ACG1 and the subordinate electric generator ACG2.
The external sensing terminals c1, c2 of the main electric generator ACG1 and the subordinate electric generator ACG2 are connected to the battery 5.
In addition, the individual power generation control devices 400 of the main electric generator ACG1 and the subordinate electric generator ACG2 are operatively connected to the key switch 6, so that they are put in a state in which their control operations become possible, by being supplied with electric currents from the starting terminal b1, b2.
As stated above, the individual power generation control devices 400 of the main electric generator ACG1 and the subordinate electric generator ACG2 carry out field current control to the field coil 2. The field current control to the field coils 2 is carried out by making a comparison between the input voltage from each of the external sensing terminals c1, c2 or each of the output sensing terminals a1, a2, and the target voltage value of the power generation voltage based on the reference voltage of each of the comparators 406 (refer to FIG. 7).
At this time, a variation at the time of production exists in the target voltage value of each of the power generation control devices 400 of the main electric generator ACG1 and the subordinate electric generator ACG2, and hence, one of the electric generators having one of the power generation control devices with a lower target voltage value first begins to interrupt the field current to the field coil 2, and the other electric generator having the other power generation control device with a higher target voltage value has a longer period of time to supply the field current to the field coil 2.